In nuclear reactor heat transport systems, thermal expansion produces stress in the pipes which carry the reactor core coolant from the reactor to the pump and heat exchanger and thence back to the reactor. In conventional piped liquid metal fast breeder reactor (LMFBR) systems, the pipe runs are generally made in long loops and the pump and intermediate heat exchanger (IHX) are solidly fastened to the building structure. With this arrangement the long pipe is capable of deflections sufficient to permit the increase in the pipe length due to thermal expansion without producing unacceptably high stresses in the pipe, but the long pipe is expensive in pipe costs and building space. In the heat transport systems of water reactors, components such as the steam generator and pumps are mounted on columns having pivoted ends. A pivot consists of a clevis, a pin, and eye with a spherical bushing between the pin and eye. When all columns are vertical there exists little load on the pipes, but when a thermal change occurs that causes the pipes to push the components laterally, and the columns are no longer vertical, the loads on the pipes become large. The pipes are not excessively stressed because of their heavy wall, but a similar system for an LMFBR would be unacceptable because the pipe walls of an LMFBR must be relatively thin to avoid thermal stress fatigue of walls.
It has been desirable for some years to provide a system that would support the components of the LMFBR heat transport system, such as the pump and IHX, in a manner that would require only a small lateral force to move the component so that thin pipes could provide that force without excessive stress. There have been two problems with the design of such a system: (1) it must have very low friction and (2) it must have very low probability of a failure that causes the system to develop excessive friction loads. Under all likely events such as, for example, hydraulic electrical failure, the system must not develop large friction.
Several solutions to the above problems have been proposed. Some are given below:
1. Mount the component on very long columns with ball joints at the column ends. With this solution the columns must be quite long to reduce lateral loads under all conditions of component position to acceptable values. For example, if a 770,000 pound component were displaced 3.5" it would exert about 660 pounds on the pipe if it were mounted on 340 foot long columns.
2. Hang the component on very long tension members. The problem here is the same as for the first solution.
3. Mount the component on hydrostatic pads. This could be made to function, but its failure mode of hydraulic pressure loss, due to leakage or electrical failure, is unacceptable.
4. Another possible solution would be to support the component with columns in which the top of the columns is a portion of a large diameter sphere. However, maintenance is difficult and could be required frequently. Also reliability is less than with the solution of the present invention.
5. Still another solution would be to support the component with columns in which the top of the column is a ball joint and the bottom of the column is a sector of a large diameter sphere. There will be less maintenance difficulty for this solution, but friction will be on the high side.